[Extensions] Add support for persistent callback listener

This is going to be the base of the EventTarget implementation. It is
important to remove the listener at some point otherwise the object will
leak.
[Extensions] Add browsertests for the persistent callback listener

The test implements a heartbeat which works in a similar way of an EventTarget.
The callback is set only one and gets called multiple times.
[Extensions] Remove development debug statements

These debugging statements were useful during development, but now
as we are feeling confident that everything should be working, they
can be removed.
Merge pull request #1039 from vcgomes/remove-development-debugs

[Extensions] Remove development debug statements
Merge pull request #1038 from tmpsantos/persistent_callback

[Extensions] Support for persistent callback
[Android] Enable the geolocation feature, add test cases.

Enable the geolocation feature by responding the request permission from
the content module, implementing the geolocation prompt in the callback functions.

Some files were copied from the android_webview, like as InMemorySharedPreferences.java,
runtime_geolocation_permission_context.cc. They were modified according to the current
project requirements, remove the jni dependency, since this feature is required on
other platforms.

For the GeolocationPermissionShowPrompt, there is a relative test case.
For the GeolocationPermissionHidePrompt, there is no test case currently.

BUG=
TEST=build/android/run_instrumentation_tests.py --test-apk XWalkCoreTest \
--verbose -I --num_retries=1 -f testGeolocationPermissionShowPrompt